Recent advances in airway imaging using micro-computed tomography and computed tomography for chronic obstructive pulmonary disease

Abstract

Chronic obstructive pulmonary disease (COPD) is a complex lung disease characterized by a combination of airway disease and emphysema. Emphysema is classified as centrilobular emphysema (CLE), paraseptal emphysema (PSE), or panlobular emphysema (PLE), and airway disease extends from the respiratory, terminal, and preterminal bronchioles to the central segmental airways. Although clinical computed tomography (CT) cannot be used to visualize the small airways, micro-CT has shown that terminal bronchiole disease is more severe in CLE than in PSE and PLE, and micro-CT findings suggest that the loss and luminal narrowing of terminal bronchioles is an early pathological change in CLE. Furthermore, the introduction of ultra-high-resolution CT has enabled direct evaluation of the proximal small (1 to 2-mm diameter) airways, and new CT analytical methods have enabled estimation of small airway disease and prediction of future COPD onset and lung function decline in smokers with and without COPD. This review discusses the literature on micro-CT and the technical advancements in clinical CT analysis for COPD. Hopefully, novel micro-CT findings will improve our understanding of the distinct pathogeneses of the emphysema subtypes to enable exploration of new therapeutic targets, and sophisticated CT imaging methods will be integrated into clinical practice to achieve more personalized management.

Keywords: Airway obstruction; Emphysema; Pathology; Pulmonary disease, chronic obstructive; Tomography, X-ray computed.

Figure 1

Ultra-high-reso lution computed tomography images of airways in smokers with and without chronic obstructive pulmonary disease (COPD). (A) Airway tree in a smoker without COPD. Longitudinal paths for the airway tree were extracted, and (B) cross-sectional ultra-high-resolution computed tomography (U-HRCT) images of airways were constructed. (C) Airway tree and (D) cross-sectional images of the airways in a smoker with COPD. The lumina were smaller than in the smoker without COPD. The third-generation airway indicates the right lower posterior segmental airway. A phantom study [22] showed that the lumen area of airways with diameters > 1 mm can be measured accurately on U-HRCT images. Scale bar, 10 mm. FEV1, force expiratory volume in 1 second; FVC, force vital capacity.

Figure 2

Airway trees and lungs in smokers with different degrees of airflow limitation. Airway trees and lungs were extracted from computed tomography images. (A) Smoker without airflow limitation. (B) Smoker with chronic obstructive pulmonary disease (COPD) and moderate airflow limitation. (C) Smoker with COPD and severe airflow limitation. The total airway count (TAC) and airway volume to lung volume ratio (AWV%) were lesser in case C than in case A. The AWV% was calculated using the volume of the airway tree, excluding the trachea. FEV1, force expiratory volume in 1 second; FVC, force vital capacity.